More precise radiation therapy lets prostate cancer patients avoid erectile dysfunction

01/06/05

Additional imaging tests help spare critical vessels, preserve sexual function

ANN ARBOR, Mich. -- Researchers at the University of Michigan Comprehensive Cancer Center are using innovative planning techniques to help men with prostate cancer avoid erectile dysfunction after radiation treatment.

By using MRI scans in addition to CT scans, radiation oncologists can identify the blood vessels that control erectile function and plan treatment to target the prostate more precisely, sparing those nearby vessels. Results from an initial study with 25 patients appear in the January issue of the International Journal of Radiation Oncology Biology Physics.

Some 230,000 men were diagnosed with prostate cancer in 2004. While it's more common in older men, a growing number of men are being diagnosed in their 50s.

"As we treat younger men, erectile function is an important concern. We're often treating men in their 50s, and this is a very important issue for them. Most of the men I see are going to be cured. Once you start curing cancers at an extremely high rate, then the focus moves to quality of life," says Patrick W. McLaughlin, M.D., clinical professor of Radiation Oncology at the University of Michigan Medical School and director of Providence Hospital Radiation Oncology, with cancer centers in Southfield and Novi, both affiliated with the U-M Comprehensive Cancer Center.

Treatment for prostate cancer can involve surgery to remove the prostate or radiation therapy. During surgery, the nerves that control erectile function may be severed which has led to new surgical techniques to avoid cutting those nerves.

But doctors are less sure what causes erectile dysfunction after radiation therapy. Erectile dysfunction among men without prostate cancer is most commonly caused by a problem in the blood vessels, and doctors do know that radiation causes obstruction of the vessels that fall within the treatment area. Using that as a starting point, the U-M team began investigating radiation-related erectile dysfunction as a blood vessel problem.

Typically, radiation oncologists rely on a CT scan to identify the prostate and plan treatment. But because of limitations in the CT scan, the images do not show the bottom of the prostate. Doctors instead estimate where the prostate ends, based on average distance from identifiable structures. The U-M study, using MRI in addition to CT scans to get a better picture of the whole prostate, found the distance between the prostate and the penile bulb ranged from 0.5 cm to 2.0 cm.

"We condemned one of the common tricks people try to use. By assuming an average distance of 1.5 cm between the prostate and the penile bulb, either you're going to treat way more than you need to or you're going to miss the prostate," McLaughlin says.

By taking the additional imaging, the U-M team was able to plan treatment to include the entire prostate but avoid the critical blood vessels below. Preliminary results suggest that avoiding the vessels prevents erectile dysfunction.

"Because we can't see any detail of this area on CT scans, we just assume if we treat below the prostate it's no big deal. But it is a big deal. There is no cancer below the prostate, but there are critical structures related to erectile function as well as urine sphincter function. Treating below the prostate may result in needless problems," McLaughlin says. "I don't have much doubt from what I've seen that this approach is likely to have huge impact."

About one in two men who undergoes radiation therapy for prostate cancer is unable to have sex five years later unless Viagra or similar medications are used.

In addition, the vessels involved in erectile function also play a role in bowel and bladder control. The researchers suspect avoiding radiation to these areas will improve other quality of life issues, such as urinary leakage and bowel problems.

In addition to McLaughlin, U-M study authors were Vrinda Narayana, Ph.D., adjunct clinical assistant professor of Radiation Oncology; Amichay Meriowitz, M.D., Sara Troyer, Peter Roberson, Ph.D., Howard Sandler, M.D., Lon Marsh, Theodore Lawrence, M.D., and Marc Kessler, Ph.D. Narayana is also affiliated with the Providence Cancer Center. Roger Gonda Jr., M.D., from Providence Hospital's Department of Radiology is also a study author.

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